Pollution abatement is a very serious matter in the pulp and paper industry and it is important to both the paper producers and to the ecology that the waste materials discharging from the mill be maintained at a minimum and preferably eliminated. However, for practical purposes it seems to be substantially impossible to eliminate all discharges from the mill.
Currently adsorbable organic halogens (AOX) are considered an undesirable class of compounds contained in the discharge (a small fraction has been found toxic to fish). Thus reduction of AOX in the effluent to lowest possible level is desirable.
There are various schemes for reduction of AOX which include substitution of chlorine dioxide C10.sub.2 for chlorine (Cl.sub.2) in the bleaching sequence and by the use of extended delignification in the kraft process followed by bleaching using oxygen, etc. to eliminate Cl.sub.2 and minimize the amount of C10.sub.2 used in bleaching and thus substantially eliminate the chlorine from the effluent.
Various techniques have been employed for removal of the AOX evolving from the C10.sub.2 from the effluent. These techniques include ultra filtration, chemical precipitation/coagulation, ozonation, UV radiation, etc. but all of these techniques are relatively expensive and in many cases not particularly effective.
One of the most widely used methods of AOX removal is by secondary treatment systems which include aerated stabilization basins or lagoons, activated sludge processes, anaerobic/aerobic systems and fungal systems. Fungal systems are the most effective but these have only been used on a lab scale.
In most secondary treatment systems the removal mechanisms employed include air stripping of the volatile AOX and bio-degradation.